//=============================================================================
// System  : MatchKit
// File    : OptionalPattern.cs
// Author  : Fabio Bussu  (matchkit@fabiobussu.it)
// Updated : 04/16/2013
// Note    : Copyright 2013, Fabio Bussu, All rights reserved
//
// This code is published under the Microsoft Public License (Ms-PL). A copy
// of the license should be distributed with the code.  It can also be found
// at the project website: http://matchkit.codeplex.com. This notice, the
// author's name, and all copyright notices must remain intact in all
// applications, documentation, and source files.
//
// Version     Date     Who  Comments
// ============================================================================
// 1.0.0.0  04/16/2013   FB  First draft
//=============================================================================
using System;
using System.Collections.Generic;
using System.Runtime.Serialization;

namespace MatchKit.Patterns
{
	/// <summary>
	/// Provides the logic to match optionally a child pattern.
	/// </summary>
	/// <threadsafety static="true" instance="false" />
	/// <serialization binary="true" contract="true" />
	/// <conceptualLink target="cb785773-b793-4cc4-acc4-6688cdb22db6" />
	/// <conceptualLink target="0a06b2a9-5f58-409a-ba62-639cfd77bca7" />
	#if DC
	[DataContract]
	#endif
	#if SZ
	[Serializable]
	#endif
	public sealed class OptionalPattern : BasePattern
	{
		/// <summary>
		/// Initializes a new instance of the <see cref="T:MatchKit.Patterns.OptionalPattern"/> class. 
		/// </summary>
		/// <param name="item">The child pattern. See <see cref="P:MatchKit.Patterns.OptionalPattern.Item"/>.</param>
		public OptionalPattern(IPattern item)
		{
			Item = item;
		}

		/// <inheritdoc />
		public override IEnumerable<IPattern> Children
		{
			get { yield return _item; }
		}

		/// <inheritdoc />
		public override bool HasChildren
		{
			get { return true; }
		}

		private IPattern _item;
		/// <summary>
		/// Gets or sets the child pattern.
		/// </summary>
		/// <serialization member="true" />
		#if DC
		[DataMember]
		#endif
		public IPattern Item
		{
			get { return _item; }
			set
			{
				if (value == null)
					throw new ArgumentNullException("value", "Item cannot be null");
				_item = value;
			}
		}

		/// <inheritdoc />
		protected override Match OnMatch(MatchContext context)
		{
			var branch = context.Branch();
			var m = _item.Match(branch);

			if (!m.Success)
				return Optional(context, m);

			context.Commit(branch);

			return m;
		}

		/// <inheritdoc />
		public override string HelpString
		{
			get { return "Optional " + _item.HelpString; }
		}
	}
}
